A multiscale and multiphysics numerical framework for modelling of hygrothermal ageing in laminated composites

Abstract

In this work, a numerical framework for modelling of hygrothermal ageing in laminated composites is proposed. The model consists of a macroscopic diffusion analysis based on Fick's second law coupled with a multiscale FE 2 stress analysis in order to take microscopic degradation mechanisms into account. Macroscopic material points are modelled with a representative volume element with random fibre distribution. The resin is modelled as elasto-plastic with damage, and cohesive elements are included at the fibre/matrix interfaces. The model formulations and the calibration of the epoxy model using experimental results are presented in detail. A study into the representative volume element size is conducted, and the framework is demonstrated by simulating the ageing process of a unidirectional specimen immersed in water. The influence of transient swelling stresses on microscopic failure is investigated, and failure envelopes of dry and saturated micromodels are compared.The combination of such effects makes a purely experimental characterisation of the hygrothermal ageing phenomenon a difficult task.A number of authors have therefore advocated numerical modelling in order to simulate the hygrothermal ageing process in polymers and composites [2,3,7,8] as well as in porous materials [9]. Because the mentioned degradation effects act on the microsopic material constituents, a micromechanics approach becomes a necessity. However, it is also important to predict how such microscopic processes affect macroscopic material behaviour. Naya et al. [7] successfully used micromechanics to predict the wet properties of a unidirectional ply by fitting a mesoscale failure criterion, although the swelling phenomenon was not considered. Such a numerical homogenisation approach entails a one-way upscaling procedure after which the microscopically obtained failure envelope can be used in mesolevel analysis.However, macroscopic phenomena such as transient swelling stresses during diffusion [10] may also influence the resultant microscopic degradation processes. Joliff et al.[3] simulated the immersion of a macroscopic specimen including diffusion and differential swelling by explicitly meshing its complete microstructure. The authors demonstrated the importance of including differential swelling in the ageing model, although material failure and degradation (plasticisation and interface weakening) were not included. However, such a DNS approach becomes computationally infeasible if an iterative failure analysis is performed at the same time.In order to simultaneously account for macroscopic transient phenomena and microscopic failure mechanisms, a concurrent multiscale approach can be chosen by solving finite element problems at both macroscale and microscale and coupling them through homogenisation by means of a so-called FE 2 approach [11]. A large body of literature is dedicated to the treatment of pure stress analysis in FE 2 [12,13], including consistent treatment of material failure across scales [14] and modelling of processes...

A combined experimental/numerical investigation on hygrothermal aging of fiber-reinforced composites

“…Fiber-matrix interface debonding is modeled using interface elements with softening behavior dictated by a cohesive-zone model. The model used in this work is based on the one presented in [18] but is modified to include a friction component, following the formulation by Alfano and Sacco [33]. The displacement jump is additively split into elastic and friction contributions:…”

“…The microscopic material models of Section 4.1 are used in conjunction with a multiscale/multiphysics framework in order to predict the behavior of macroscopic material specimens subjected to aging followed by mechanical loads. The framework is presented in detail in [18] and will be briefly summarized in the following.…”

“…This paper presents a combined experimental and numerical investigation on hygrothermal aging of a glass/epoxy composite system. The work builds upon previous experimental [7] and numerical [18] studies performed by the authors, combining them and including a number of relevant improvements. For the experimental part, a new set of mechanical tests is performed on purely unidirectional short-beam specimens aged in demineralized water at 50 • C for different durations in order to track the evolution of material degradation, including tests on samples redried after having been both partially and fully saturated.…”

“…Macroscopic behavior can in turn be obtained through a bottom-up numerical homogenization procedure [1,3] after which the micromodel is substituted by a calibrated mesoscale model. Alternatively, both scales can be treated concurrently through computational homogenization (FE 2 ) [17][18][19]. This approach allows for realistic modeling of macroscopic structures with non-uniform degradation states without any mesoscale constitutive assumptions.…”

“…For the numerical study, the multiscale and multiphysics numerical framework proposed in [18] is improved by including a new viscoelastic/viscoplastic/damage constitutive model for the resin [23] and a cohesive-zone model with friction for the fibermatrix interfaces. Furthermore, the full-order microscopic boundary value problem embedded at each macroscopic material point is substituted by a hyper-reduced model constructed using two different model order reduction techniques [24].…”